1. Technical Field
This invention relates to a test method that is can assess the quality of video sequences, in particular digitally encoded video signals.
2. Related Art
In order to reduce the bandwidth necessary to carry video sequences, compression algorithms such as H263 or MPEG rely on a set of well known methods. The first of these is to suppress the information present in each frame that is not perceptually relevant. The result of this operation may not be perceptible to the end user, perceptible but not perceptually relevant, or disruptive to the information content of the frame. In most cases, the effect of the information suppression will be to modify the appearance of textured objects, giving a greater repetitiveness or simplicity.
In real world applications, where the video quality has to be assessed continuously, it can be very difficult or costly to provide a system with a test signal, and the test signal will be transmitted through the system under test. For these reasons, non-intrusive systems have been investigated, where only a reconstructed signal is needed. How can we know the quality of a video sequence that is assessed without being able to determine what has been added to or removed from it? However, just as a subjective viewer knows what quality of video sequence can be expected from a television set, most people are able to make a judgement of quality without referring to the original image. More advanced or experienced users of the system will also know the type of degradation introduced by the medium they use, and will be able to spot such degradations to make a more educated estimation of the quality. Similarly, it is known that each family of compression algorithms tends to introduce its own type of distortion with respect to what can be expected from natural images. This information can be used to determine what amount of distortion has been added to a sequence without referring to its original.